Various power tools are used in woodworking in an effort to efficiently and accurately form workpieces to desired dimensions and with a desired surface finish. As is widely known, planing machines are often used for surface planing of wooden boards. A conventional planing machine typically includes one or more rotatably mounted cutting blades attached to a vertically movable carriage assembly. Also known are jointer machines which are typically used for the edge planing of wood. In certain applications, the functions of conventional planing machines and jointers are combined within a single unit commonly referred to as a jointer/planer machine. 
In a typical wood planing machine, such as a surface planer, a selectively adjustable workpiece opening is defined between a carriage assembly and the planing surface of the base of the machine. The rotationally mounted blades are carried on the underside of the carriage assembly adjacent to the workpiece opening. The blades are adapted to remove a predetermined amount of material from the workpiece depending on the thickness of the workpiece and the height of the workpiece opening. The carriage assembly also usually includes one or more feed rollers which urge the workpiece through the workpiece opening during the operation of the wood planing machine.
In most applications, the carriage assembly of a wood planing machine is movably mounted to a plurality of support columns for movement with respect to the planing surface. Such movement of the carriage assembly adjusts the vertical dimension of the workpiece opening so as to selectively determine the amount of material to be removed from the workpiece. Alternatively, the carriage assembly may be fixed and the planing surface adjusted vertically with respect to the carriage assembly so as to adjust the vertical dimension of the workpiece opening.
In use, a workpiece is passed through the workpiece opening and a predetermined amount of material is removed from the surface of the workpiece adjacent the carriage assembly. Multiple passes of the workpiece through the workpiece opening are often necessary to obtain the desired thickness and surface finish. As with other woodworking operations, it is desirable that a planing machine accomplishes preparation with precision, repeatability and a high quality surface finish.  In order to accomplish these goals, many of the planing machines of the prior art have relied on designs that utilize rather large and heavy components.
While such designs have proven to be acceptable for relatively large planing machines which are repositioned on a relatively infrequent basis, they have largely been inadequate for portable planing machines, due to their weight. Accordingly, there is a need in the art for a portable planing machine having a highly robust design that permits a workpiece to be prepared with precision, repeatability and a high quality surface finish.